Glass is desirable for numerous properties and applications, including optical clarity and overall visual appearance. For some example applications, certain optical properties (e.g., light transmission, reflection and/or absorption) are desired to be optimized. For example, in certain example instances, reduction of light reflection from the surface of a glass substrate may be desirable for storefront windows, display cases, photovoltaic devices (e.g., solar cells), picture frames, other types of windows, and so forth.
Photovoltaic devices such as solar cells (and modules therefor) are known in the art. Glass is an integral part of most common commercial photovoltaic modules, including both crystalline and thin film types. A solar cell/module may include, for example, a photoelectric transfer film made up of one or more layers located between a pair of substrates. One or more of the substrates may be of glass, and the photoelectric transfer film (typically semiconductor) is for converting solar energy to electricity. Example solar cells are disclosed in U.S. Pat. Nos. 4,510,344; 4,806,436; 5,977,477; 6,123,824; 6,288,325; 6,506,622; 6,613,603; and 6,784,361, and JP 07-122764, the disclosures of which are hereby incorporated herein by reference.
Substrate(s) in a solar cell/module are sometimes made of glass. Incoming radiation passes through the incident glass substrate of the solar cell before reaching the active layer(s) (e.g., photoelectric transfer film such as a semiconductor) of the solar cell. Radiation that is reflected by the incident glass substrate does not make its way into the active layer(s) of the solar cell, thereby resulting in a less efficient solar cell. In other words, it would be desirable to decrease the amount of radiation that is reflected by the incident substrate, thereby increasing the amount of radiation that makes its way to the active layer(s) of the solar cell. In particular, the power output of a solar cell or photovoltaic (PV) module may be dependant upon the amount of light, or number of photons, within a specific range of the solar spectrum that pass through the incident glass substrate and reach the photovoltaic semiconductor.
Because the power output of the module may depend upon the amount of light within the solar spectrum that passes through the glass and reaches the PV semiconductor, certain attempts have been made in an attempt to boost overall solar transmission through the glass used in PV modules. One attempt is the use of iron-free or “clear” glass, which may increase the amount of solar light transmission when compared to regular float glass, through absorption minimization.
In certain example embodiments of this invention, an attempt to address the aforesaid and/or other problem(s) is made using an antireflective (AR) coating on a glass substrate (the AR coating may be provided on either side of the glass substrate in different embodiments of this invention). An AR coating may increase transmission of light through the light incident substrate, and thus the power of a PV module in certain example embodiments of this invention.
Certain example embodiments of this invention relate to a method of making a coated article. A glass substrate is provided. A sol is prepared, with the sol comprising colloidal silica having a particle size of 10-110 nm. The sol is spin coated, directly or indirectly, onto the glass substrate. The sol is cured to form a silica-inclusive anti-reflective (AR) coating. The glass substrate together with the AR coating is heat treated at a temperature of at least about 500 degrees C. Oost heat treatment, the AR coating has a b* value of 0.8 or greater.
In certain example embodiments, the preparing of the silica sol comprises: (1) preparing a polymeric component, the polymeric component comprising n-propanol, Glycydoxylpropyltrimethoxysilane (Glymo), water, and hydrochloric acid; (2) mixing the polymeric component; (3) forming a coating solution by combining the polymeric solution with the colloidal silica in methyl ethyl ketone; and (4) stirring the coating solution to form the silica sol.
In certain example embodiments, the glass substrate together with the AR coating is built into a photovoltaic device or another suitable electronic device.
Certain example embodiments of this invention relate to a method of making a solar cell. A glass substrate is provided. A sol comprising colloidal silica having a particle size of 10-110 nm is spin coated, directly or indirectly, onto the glass substrate. The sol is cured to form a silica-inclusive anti-reflective (AR) coating. The glass substrate together with the AR coating is heat treated at a temperature of at least about 500 degrees C. Post heat treatment, the AR coating has a b* value of 0.8 or greater and the AR coating provides a visible transmission gain of at least about 2.5% relative to the glass substrate alone.
In certain example embodiments, the curing comprises exposing the substrate together with the sol spin coated thereon to first and second elevated temperatures, the second elevated temperature being higher than the first elevated temperature.
Certain example embodiments of this invention relate to a coated article comprising a heat treated glass substrate and an AR coating spin coated from a sol comprising colloidal silica having a particle size of 10-110 nm, directly or indirectly, onto the substrate. The AR coating has a b* value of 0.8 or greater, and the AR coating provides a visible transmission gain of at least about 2.5% relative to the glass substrate alone.
In certain example embodiments, the colloidal silica particles may be uniformly or substantially uniformly sized. In certain example embodiments, the colloidal silica particles may be differently sized with respect to one another.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.